Nowadays, cellular phones have become pervasive not only in Japan but also all over the world. Many of currently popularized cellular phones comprise a housing provided with display means and a housing provided with input means, where these housings are coupled such that they are capable of displacement relative to each other. For example, a housing provided with a display device (upper housing) and a housing provided with an input device (lower housing) are coupled through a hinge mechanism such that they can make pivotal movements. More specifically, a liquid crystal display is housed in the upper housing, and a display screen of the display is exposed on a front surface of the upper housing. On the other hand, the input device is incorporated in the lower housing, and input keys, which serve as an interface of the input device, are arranged on a front surface of the lower housing. Then, the upper housing and lower housing are coupled for pivotal movements from a state where the front surfaces thereof oppose each other to a state where both the front surfaces form an angle of approximately 160°. Further, with improvements in functions, some cellular phones which have come on the market comprise two or more housings which can make pivotal movements or sliding movements in various directions.
Here, since cellular phones may be used in dark places, many of them additionally comprise a light source for illuminating input keys from a back side thereof. For example, a known cellular phone incorporates a light source such as a light emitting diode (LED) in a housing which is provided with input keys, at least part of input keys are made of translucent material. In such a cellular phone, since light emitted from the light source passes through the input keys, one can view characters, symbols and the like displayed on the surfaces of the input keys even in dark places.
Also, JP2004-220113A (Document 1) and JP2006-5410A (Document 2) disclose cellular phones which comprise a light source for illuminating input keys from a front side thereof. The cellular phone disclosed in Document 1 comprises a first housing provided with a keyboard unit, a second housing provided with a display unit, and a hinge section for coupling the two housings to allow them to open/close. Additionally, a high-luminance light emitting diode is incorporated within the hinge section. The hinge section further comprises a lens fixed thereto, which comprises a first lens section oriented toward the display unit and a second lens section oriented toward the keyboard unit. Then, when the two housings are open, light emitted from the high-luminance light emitting diode is guided to the keyboard unit by the second lens section, so that the keyboard unit is illuminated from the front side thereof.
The cellular phone disclosed in Document 2 comprises a first housing which has a display panel arranged thereon, and a second housing which has a key operating portion, including a plurality of keys, arranged thereon. These two housings are coupled by a hinge mechanism for rotation relative to each other in the horizontal direction. The first housing is also provided on a side surface with a lighting unit including LED (light emitting diode). Then, the lighting unit functions as a key operating portion illumination light source for illuminating the key operating portion provided to the second housing when the two housings remain open.